Weeds occurrence and importance under distinct intercropping systems

Intercropping systems involving corn are often subjected to stress caused by weeds, which usually result in 30-70 per cent yield loss when no control practice is applied. This study aimed to assess the composition of weed communities due to soil coverage, at neighboring areas submitted to distinct soil managements. The soil was collected at field and the study was conducted under a greenhouse in three steps: (1) weeds composition and importance within each treatment; (2) comparison between treatments (distinct crop and intercropping managements); (3) infestation in the area as a whole. The weed composition in the short term is influenced by the management of the area, but this shift requires some more years to be reflected at the soil seed bank. Some weed species occur in high densities and even this way they may not be the most serious weed species present in a given field. Just a few species are adapted to a given system of management in a level enough to be a troublesome weed. Areas differed in relation to weed infestation as a function of management adopted and number of years the new management was applied.

Weeds under the canopies of tree species submitted to different planting densities and intercropping

Assessing the growth and floristic composition of species that grow under the canopy of trees is important for weed control (WC). The objective of this study was to assess two experiments (E1 and E2), when the trees were two years and one year of age, respectively. In E1, sabiá (S) and gliricidia (G) were submitted to planting densities from 400 to 1.200 plants ha-1. In E2, growing systems consisting of S, G, and neem (N) combinations were compared: SSS, GGG, NNN, GSG, NSN, SGS, NGN, SNS, and GNG (each letter represents a row of plants). A random block design was adopted, with three (E1) and four (E2) replicates. In E1, treatments were arranged as split-plots (species in plots). In E2, the degrees of freedom for treatments (8) were partitioned into growing systems (treatments that involved the same species) and between growing system groups (2). Twenty-one weed species were found in E1. Gliricidia attained greater plant height than sabiá, but these species did not differ in canopy diameter, number of weed species per plot, and weed green and dry biomass of the shoot. Higher planting densities resulted in the reduction of all those traits. Twenty-six weed species were found in E2. Growing systems that included gliricidia showed canopies with greater diameters than growing systems that included neem. There were no differences between growing systems for number of weed species per plot and for weed green and dry biomass of the shoot.

Corn cultivar intercropping with arboreal legumes for weed control

Gliricidia (Gliricidia sepium) seedlings are usually beneficial to corn crops when planted between corn rows. The objective of this work was to assess the effects of corn intercropped with gliricidia and "sabiá" (Mimosa caesalpiniifolia), a species native to the Brazilian northeastern region, on weed control and corn green ear and grain yields. The experiment was carried out at Estação Experimental da Universidade Federal Rural do Semi-Árido - UFERSA (Mossoró, State of Rio Grande do Norte, Brazil). The experimental design consisted of randomized complete blocks (multifactorial design) with five replications, arranged in split-plots. The plots consisted of corn cultivars AG1051 and BM 2022; subplot treatments (six) were no-hoeing, twice-hoeing (at 20 and 40 days after sowing) and intercropping with gliricidia and "sabiá", either directly sown or transplanted, simultaneously with corn sowing. The intercropped leguminous plants were spaced 0.40 m from each other, and directly seeded or transplanted (30-day-old seedlings) in between two 1 m-spaced corn rows. Twenty three weed species were identified during the experiment. Gliricidia seedlings were superior to "sabiá" seedlings with regard to plant height and survival rate. The highest corn green ear and grain yields were found for twice-hoed subplots, while the lowest yield was found for no-hoed or intercropped subplots. However, grain yield values in intercropped treatments did not differ from grain yield values in hoed plots. In addition, marketable husked green ear mean weights did not differ between twice-hoed subplots and subplots directly seeded with gliricidia and "sabiá". Such results indicated that corn benefited from the intercropping system, but intercropping with gliricidia and "sabiá" transplanted resulted in lower benefits than with the direct sowing of those species.

Occurrence of weed species in Jatropha curcas intercropping systems

This study aimed to evaluate the level of infestation by weed species in a consolidated Jatropha plantation, as a function of the plant species grown in interrows. The experiment was installed in 2006 at the district of Itahum, city of Dourados, state of Mato Grosso do Sul, Brazil, made possible through a partnership between Embrapa Western Agriculture and Paraiso Farm. Treatments consisted of (1) Jatropha in monocrop, with no plant at the interrrows; or the following plants cultivaded at the interrows of Jatropha: (2) Stylosanthes spp.; (3) Brachiaria ruziziensis; (4) Brachiaria ruziziensis + Stylosanthess pp.; (5) Brachiaria humidicola; (6) Panicum maximum cv. massai; (7) Cajanus cajan cv. anão; (8) Crotalaria spectabilis; (9) Crop rotation system 1 - (maize second crop -Crambe abyssinica - soybean - peanut); and (10) Crop rotation system 2 - (cowpea - radish - maize - cowpea) conducted for two years. Phytosociological characterization of weed species was accomplished in 2011 based on the Ecological Approach. Estimations of relative abundance, frequency, dominance and Importance Value Index were obtained. Areas were also characterized by the diversity coefficients of Simpson and modified Shannon-Weiner, and then grouped by cluster analysis. Areas with low soil coverage resulted in higher infestation levels; crop rotation in the interrows of Jatropha produced a significant reduction in weed infestation, but the lowest infestation levels were observed when grasses were grown intercropped with Jatropha. Lower diversity coefficients were associated with occurrence of the most troublesome weed species. In the first years after planting Jatropha, species of Brachiaria or a crop rotation involving species with high mulching ability and whose biomass exhibit a high C:N ratio, should be established in the interrows to avoid problems with weeds infestation.

Weed Control in Maize with Gliricidia Intercropping

One of the very important components in the organic maize production costs refers to spending on weed control. In this research were assessed the effects of maize hybrids (AG 1051 and BR 205) in an intercropping with Gliricidia (Gliricidia sepium) and mechanical hoeing on weed control. The treatments assessed were: A - maize monocropping + two hoeings (20 and 40 days after sowing); B - maize with one hoeing at 20 days + intercropping with gliricidia sowed after hoeing; C - maize sowing intercropped with gliricidia at the time of maize sowing + hoeing at 40 days; D - maize sowing intercropped with gliricidia at the time of maize sowing without hoeing; E - monocropping maize without hoeing. In the intercroppings, gliricidia was sowed in broadcast seeding with 30 viable seeds m-2. Maize hybrids did not differ in their effects on weed growth and grain yield. Treatments A, B and C have reduced weed growth, compared to treatments D and E. The highest grain yield was obtained with treatment A and the lowest with treatment E. It was concluded that intercropping maize and gliricidia is not a good alternative for an integrated weed management in maize crops in the conditions assessed.

INTERCROPPING CORN WITH A COMBINATION OF TREE SPECIES TO CONTROL WEEDS

ABSTRACT The combination of crop residues or crop extracts is often more advantageous in controlling weeds, than the application of each residue or extract singly. This suggests that in intercropping with maize, the combination of tree species can be more advantageous than species isolated in weed control. The objective of this study was to evaluate the effects of intercropping with a combination of leguminous on the weed growth and corn yield. A randomized-block design with split plots (cultivars in plots) and five replicates was established. The cultivars BR 205 and AG 1041 were subject to the following treatments: two weedings (A), intercropping with sabiá (B), gliricidia (C), gliricidia + sabiá (D) and no weeding (E). In the B and C, 30 viable seeds m-2 of the leguminous were sown. In the D, 15 seeds of each species were sown m-2. The legumes were sown by random casting during corn planting. The sequence of the best treatments in reducing the growth of weeds is A > B = C = D = E. The sequence of the best treatments when are considered the yields of baby corn, green corn and grain is A > B > C > D > E. The cultivars do not differ in regards to the reduction in weed growth. In terms of corn yield cultivar BR 205 is the best.

Glyphosate Herbicide Use in Urochloa brizantha Management in Intercropping With Herbicide-Resistant Maize

The success of the intercropping among cultivated species depends on the adoption of practices that provide, in due course, greater competitive ability of a species over another. The objective of this study was to evaluate the use of glyphosate herbicide in the suppression of Brachiaria (signalgrass) intercropped with maize. The experiment was conducted in a randomized complete block design with four replications. The treatments were arranged in a 5 x 2 + 2 factorial arrangement, the first factor corresponding to the doses of glyphosate (48, 96, 144, 240, 480 g ha-1 of the acid equivalent (a.e)) and the second one to the vegetative stages of the signalgrass at the time of application (2 and 4 tillers). Two controls were added to the treatment list, comprising controls without herbicide application and hand removal of the signalgrass. The number of plants, tillers and dry matter of signalgrass was reduced with glyphosate. The increase of the glyphosate doses enhanced the injure to the forage plants, mainly when the compound was sprayed at the two-tiller vegetative stage. The dry matter of maize plants increased proportionally to the glyphosate dose. However, the height of the maize plants was not affected. The grain mass and productivity of maize grain increased with increasing dose of glyphosate. The maize yield was negatively influenced on the untreated control. Glyphosate at 96 and 144 g ha-1, when applied at 2 and 4 tiller stage, respectively, reduces the growth of signalgrass and does not affect the maize grain yield.

Interactions of onion (Allium cepa) and yellow wax bean (Phaseolus vulgaris) in monoculture and intercropping with weeds, Chenopodium album and Amaranthus hybridus

Intercropping systems are seen as advantageous as they can provide higher crop yield and diversity along with fewer issues related to pests and weeds than monocultures. However, plant interactions in intercropped crop species and between crops and weeds in these systems are still not well understood. The main objective of this study was to investigate interactions between onion (Allium cepa) and yellow wax bean (Phaseolus vulgaris) in monocultures and intercropping with and without the presence of a weed species, either Chenopodium album or Amaranthus hybridus. Another objective of this study was to compare morphological traits of C. album from two different populations (conventional vs. organic farms). Using a factorial randomized block design, both crop species were planted either in monoculture or intercropped with or without the presence of one of the two weeds. The results showed that intercropping onion with yellow wax bean increased the growth of onion but decreased the growth of yellow wax bean when compared to monocultures. The relative yield total (RYT) value was 1.3. Individual aboveground dry weight of both weed species under intercropping was reduced about 5 times when compared to the control. The poor growth of weeds in intercropping might suggest that crop diversification can help resist weed infestations. A common garden experiment indicated that C. album plants from the conventional farm had larger leaf area and were taller than those from the organic farm. This might be associated with specific evolutionary adaptation of weeds to different farming practices. These findings contribute to the fundamental knowledge of crop-crop interactions, crop-weed competition and adaptation of weeds to various conditions. They provide insights for the management of diversified cropping systems and integrated weed management as practices in sustainable agriculture.

Nitrogen in combination with Desmodium intortum effectively suppress Striga asiatica in a sorghum‒Desmodium intercropping system

It is well known that the parasitic weed Striga asiatica (L.) Kuntze can be suppressed by Striga-tolerant sorghum (Sorghum bicolor L. Moench) cultivars, Desmodium intortum (Mill.) Urb. (greanleaf desmodium), and by fertilization with nitrogen. The study objective was the assessment of Striga control provided by integration of Desmodium density, timing of sorghum-Desmodium intercrop establishment, and nitrogen fertilization. Growth responses and yield of three sorghum cultivars were measured in three pot experiments. A soil naturally infested with Striga was used, and that part of the soil which served as uninfested control was chemically sterilised. Striga numbers and growth were affected significantly by sorghum cultivars, sorghum-Desmodium intercrop ratios, timing of the sorghum-Desmodium association, as well as by their interactions. Desmodium caused 100% suppression of Striga emergence when Desmodium was established in the 1:3 sorghum-Desmodium ratio at seeding of sorghum. Total control of Striga was also achieved with the 1:1 sorghum-Desmodium ratio when Desmodium was transplanted 30 days before sorghum seeding. However, these two treatments also caused significant reductions in sorghum yield. In contrast, 100% Striga control and a dramatic increase in sorghum yield were achieved with 100 kg N ha^{-1} in the 1:1 sorghum-Desmodium intercrop. Compatibility of sorghum and Desmodium was evident at the 1:1 sorghum-Desmodium intercrop established at sorghum seeding. Overall, the Ethiopian cultivars Meko and Abshir showed better agronomic performance and higher tolerance to Striga than the South African cultivar PAN 8564. It is recommended that the N × Desmodium × sorghum interaction be investigated under field conditions.

Agronomic aspects of intercropping spring or winter peas and cereals as influenced by ploughing system

Ziel der vorliegenden Arbeit war es, den Mischfruchtanbau von Sommer- oder Wintererbsen und Getreide zu bewerten und die Eignung einer flachwendenden Bodenbearbeitung im ökologischen Erbsenanbau zu ermitteln. Weiterhin war im Rahmen dieser Arbeit beabsichtigt, den Einfluss einer mechanischen Bodenbelastung zur Saat auf die Leistungsfähigkeit von Sommererbsen in Reinsaat und Gemenge nach tief- (Pflug, 25-30 cm) und flachwendender (Stoppelhobel, 7-12 cm) Bodenbearbeitung zu untersuchen. Zu diesem Zweck wurden Feldversuche mit den Versuchsfaktoren Anbauform (Sommererbsen und Hafer in Reinsaat oder Gemenge), Pflugsystem (flach- und tiefwendend), mechanische Bodenbelastung (0 t; 2,6 t; 4,6 t Hinterradlast) und Standort (Köllitsch, Trenthorst) in 2009 und 2010 durchgeführt. Der Mischfruchtanbau zweier Wintererbsen-Sorten (E.F.B. 33: normalblättrig, buntblühend; James: halbblattlos, weißblühend) nach flach- und tiefwendender Bodenbearbeitung wurde am Standort Trenthorst in den Jahren 2009/10 und 2010/11 untersucht. Zur Untersuchung der Vorfruchtwirkung wurde im Anschluss an die Wintererbsen-Versuche Winterweizen angebaut. Ein Gefäßversuch und ein Bioassay wurde ergänzend zu den Mischfruchtversuchen mit Sommererbsen durchgeführt, um die Ursachen eines unterschiedlichen Unkrautunterdrückungsvermögens in Reinsaaten und Gemenge von Sommererbsen und Hafer bestimmen zu können. Mischfruchtbestände von Erbsen und Getreide unterdrückten annuelle Unkräuter stärker als Erbsen-Reinsaaten, was insbesondere bei halbblattlosen Erbsen zu beobachten war. Die Ergebnisse weisen darauf hin, dass eine stärkere unterirdische Interaktion zwischen Kulturpflanzen und Unkräutern für die stärkere Unkrautunterdrückung in Erbsen-Hafer-Gemengen im Vergleich zu Erbsen-Reinsaaten verantwortlich war. Die flachwendende Bearbeitung führte in Sommererbsen-Reinsaaten zu einem signifikant höheren Unkrautaufkommen, wohingegen in den Erbsen-Hafer-Gemengen eine vergleichbare (Köllitsch) oder signifikant höhere (Trenthorst) Verunkrautung nach flachwendender Bearbeitung vorhanden war. In den Wintererbsen-Versuchen waren keine signifikanten Unterschiede hinsichtlich des Unkrautaufkommens zwischen den Pflugsystemen festzustellen. Der Mischfruchtanbau von Wintererbsen und Triticale reduzierte den Befall mit der Grünen Erbsenblattlaus und verbesserte die Standfestigkeit der normalblättrigen Wintererbse, wohingegen kein positiver Effekt des Mischfruchtanbaus in Hinsicht auf Auswinterungsverluste der Wintererbsen und einen Befall mit dem Erbsenwickler festgestellt werden konnte. Die Mischfruchtbestände von Sommer- oder Wintererbsen und Getreidepartnern wiesen unter der Voraussetzung, dass keine Ertragsbildungsprobleme beim Getreide auftraten, höhere Gesamterträge im Vergleich zu den entsprechenden Erbsen-Reinsaaten auf. Die Getreidepartner unterdrückten in den Mischfruchtbeständen insbesondere die halbblattlosen Erbsen. Die flachwendende Bodenbearbeitung führte im Vergleich zur tiefwendenden Bearbeitung zu einer vergleichbaren oder signifikant besseren Ertragsleistung der Rein- und Mischfruchtbestände von Erbsen und Getreide. Die mechanische Bodenbelastung hat die Ertragsleistung und die Kornqualität der Kulturen im Jahr 2009 nicht beeinflusst. Im Jahr 2010 führte die mechanische Bodenbelastung, im Gegensatz zum Hafer, zu einer Reduzierung der Erbsen-Erträge um 12,1 % (2,6 t) und 20,8 % (4,6 t). Zudem nahmen der Rohproteingehalt der Erbsen und die Gesamterträge mit zunehmender mechanischer Bodenbelastung nach tiefwendender Bodenbearbeitung kontinuierlich ab, wohingegen nach flachwendender Bearbeitung keine signifikanten Unterschiede festgestellt wurden. Der Winterweizen, der nach den Rein- und Mischsaaten von E.F.B. 33 angebaut wurde (2010/11: 35,9; 2011/12: 20,1 dt TM ha-1), war dem Winterweizen nach den Rein- und Mischsaaten von James (2010/11: 23,8; 2011/12: 16,7 dt TM ha-1) ertraglich überlegen. Während im Jahr 2010/11 kein signifikanter Unterschied der Ertragsleistung der Nachfrucht Winterweizen in den beiden Pflugsystemen festgestellt wurde, führte die flachwendende Bodenbearbeitung im Jahr 2011/12 zu signifikant geringeren Winterweizen-Erträgen (12,9 dt TM ha-1) im Vergleich zur tiefwendenden Bodenbearbeitung (20,5 dt TM ha-1). Der metabolische Energiegehalt der weißblühenden Winter- (15,2 MJ kg-1) und Sommererbsen (15,7 MJ kg-1) lag signifikant über demjenigen der buntblühenden Wintererbsen-Sorte E.F.B. 33 (13,3 MJ kg-1). Das Pflugsystem hatte nur geringe Auswirkungen auf die Kornqualität und den energetischen Futterwert.

Intercropping with pulses to concentrate nitrogen and sulphur in wheat

The effects of intercropping wheat with faba bean (Denmark, Germany, Italy and UK) and wheat with pea (France), in additive and replacement designs on grain nitrogen and sulphur concentrations were studied in field experiments in the 2002/03, 2003/04 and 2004/05 growing seasons. Intercropping wheat with grain legumes regularly increased the nitrogen concentration of the cereal grain, irrespective of design or location. Sulphur concentration of the cereal was also increased by intercropping, but less regularly and to a lesser extent compared with effects on nitrogen concentration. Nitrogen concentration (g/kg) in wheat additively intercropped with faba bean was increased by 8% across all sites (weighted for inverse of variance), but sulphur concentration was only increased by 4%, so N:S ratio was also increased by 4%. Intercropping wheat with grain legumes increased sodium dodecyl sulphate (SDS)-sedimentation volume. The effect of intercropping on wheat nitrogen concentration was greatest when intercropping had the most deleterious effect on wheat yield and the least deleterious effect on pulse yield. Over all sites and seasons, and irrespective of whether the design was additive or replacement, increases in crude protein concentration in the wheat of 10 g/kg by intercropping with faba bean were associated with 25-30% yield reduction of the wheat, compared with sole-cropped wheat. It was concluded that the increase in protein concentration of wheat grain in intercrops could be of economic benefit when selling wheat for breadmaking, but only if the bean crop was also marketed effectively.